1. Field of the Invention
This invention relates generally to backup and archival systems, and more particularly, to a system and method for deleting partial virtual tape volumes in a virtual tape library.
2. Description of the Related Art
In the field of information technology, backup refers to the copying of data so that these additional copies may be restored after a data loss event. Backups are useful primarily for two purposes: to restore a computer to an operational state following a disaster (called disaster recovery) and to restore small numbers of files after they have been accidentally deleted or corrupted. Backups differ from archives in the sense that archives are the primary copy of data and backups are a secondary copy of data. Backup systems differ from fault-tolerant systems in the sense that backup systems assume that a fault will cause a data loss event and fault-tolerant systems assume a fault will not. Since a backup system contains at least one copy of all data worth saving, the data storage requirements can be considerable. Organizing this storage space and managing the backup process may be a complicated undertaking.
Magnetic tape is generally the most commonly used medium for bulk data storage, backup and archiving. There are myriad formats, many of which are proprietary or specific to certain markets like mainframes or a particular brand of personal computers. A tape drive is a data storage device that reads and writes data stored on a magnetic tape or a punched tape. It is typically used for archival storage of data stored on hard drives. Tape media generally has a favorable unit cost and long archival stability.
Instead of allowing random-access to data as hard disk drives do, tape drives only allow for sequential-access of data. A hard disk drive can move its read/write heads to any random part of the disk platters in a very short amount of time, but a tape drive must spend a considerable amount of time winding tape between reels to read any one particular piece of data. As a result, tape drives have very slow average seek times. Despite the slow seek time, tapes drives can stream data to tape very quickly.
A tape library is a storage device that may contain tape drives, slots to hold tape cartridges and an automated method for physically moving tapes within the device. These devices can store immense amounts of data. A Virtual Tape Library (VTL) is a data storage virtualization technology used typically for archival and backup purposes. In generic terms, a VTL presents a storage component (such as disk) as tapes available for use with tape drive and media changer emulations. In other words, a Virtual Tape Library (VTL) is a storage device that appears to be a tape library to backup software, but actually stores data by some other means. A VTL can be configured as a temporary storage location before data is actually sent to real tapes or it can be the final storage location itself.
Virtualizing the storage as tape hardware allows integration of VTLs with existing archiving policies and backup software while taking advantage of the benefits of storage virtualization. The benefits of tape virtualization include storage consolidation and faster data restore processes.
Most current VTL solutions use ATA or SATA disk arrays as the primary storage component due to their relatively low cost. By backing up data to disks instead of tapes, VTL often increases performance of both backup and recovery operations. In some cases, the data stored on the VTL's disk array is exported to other media, such as tapes, for disaster recovery purposes.
Small Computer System Interface (SCSI) is a standard interface and command set for transferring data between devices on both internal and external computer buses. SCSI is most commonly used for hard disks and tape storage devices, but also connects a wide range of other devices, including scanners, printers, CD-ROM drives, CD recorders, and DVD drives. In fact, the entire SCSI standard promotes device independence, which means that theoretically SCSI can be used with any type of computer hardware.
Fibre Channel is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards (INCITS), an American National Standard Institute-accredited standards committee. It started for use primarily in the supercomputer field, but has become the standard connection type for storage area networks in enterprise storage. Despite its name, Fibre Channel signaling can run on both twisted-pair copper wire and fiber optic cables.
Traditionally, backup applications store backup images to tape volumes and generally expire backup images after a certain amount of time. In other words, an individual backup image may only be considered valid or necessary for a certain amount of time, generally until another version of the data needs to backed up. Generally, a tape volume may not be overwritten until all the backup images on that particular tape volume have expired. Traditional tape systems, including traditional virtual tape libraries have no mechanism for delete data associated with, or corresponding to, expired backup images. Instead, the expired backup images are overwritten after the entire tape volume has been expired and the backup software begins overwriting the expired tape volume. Additionally, traditional tape systems only overwrite tape volumes, and therefore backup images, starting at the beginning of the tape volume and proceeding sequentially.